Double-acting tandem piston pump

ABSTRACT

A high pressure tandem piston pump reciprocated by pressured oil from a vehicle engine driven hydraulic pump to surge water at high pressure from a vehicle tank or other source through a hose and nozzle to create a jumping action or jack hammer driving of the nozzle forcing it through and around obstructions in a sewer pipe. The engine driven pump pumps oil to opposite sides of one of the pistons of the tandem pump causing it to reciprocate the piston for high pressure surging delivery of water. Oil flow to opposite sides of the driving piston to is controlled from a valve tripped by a switch which is actuated by a control rod slidable in a recess of the connecting rod between the two pistons of the tandem pump and arranged to be pushed to a switch tripping position at one end of the stroke of the pump admitting high pressure oil which further ejects the control rod and holds it in an extended position until pulled to a retracted locked position at the opposite end of the stroke of the pump permitting the switch to again be tripped for reversing the flow from the engine driven pump.

United States Patent Shaddock 51 Oct. 24, 1972 [54] DOUBLE-ACTING TANDEMPISTON PUMP Primary Examiner-Robert M. Walker 72] Inventor: Roland E.Shaddock, Streator, m. Ammey-Cam [73] Assignee: Myers-Sherman Company,Streator, [57] ABSTRACT A high pressure tandem piston pump reciprocatedby [22] Filed: Aug. 23, 1971 pressured oil from a vehicle engine drivenhydraulic pump to surge water at high pressure from a vehicle Appl' tankor other source through a hose and noule to R A can i create a jumpingaction or jack hammer driving of the elated pp n Dam nozzle forcing itthrough and around obstructions in a [62] Division of Set. N0. 857,424,Sept. 12, 1969, sewer pipe, The engine driven pump pumps oi] t p- Pat.No. 3,658,589. posite sides of one of the pistons of the tandem pumpcausing it to reciprocate the piston for high pressure [52] US. Cl..Al7l404, 417/390, 91/275 surging delivery of water. Oil flow toopposite sides of [51] int. Cl.......F04b 9/08, F04b 17/00, F04b 35/00,the driving piston to is controlled from a valve tripped Foll 25/08 by aswitch which is actuated by a control rod slidable [5s] Fieldolsearch........417/390, 404;91/27s, 313, in a recess of the wnnectins rodbetween the two 334 pistons of the tandem pump and arranged to be pushedto a switch tripping position at one end of the [56] New and stroke ofthe pump admitting high pressure oil which further ejects the controlrod and holds it in an ex- UNITED STATES PATENTS tended position untilpulled to a retracted locked posi- 2,087,713 7/1937 Whiteside et al......417/404 x 9". 9 9 the 9" 'P 2 854 826 [0/1958 Johnston 417/404mlttmg the switch to again be tripped for reversmg the n f th d I2,726,490 12/1955 Lowe ..91/275 x W mm e engme Pump 2,842,108 7/1958Sanders ..l23/ 102 7 Claims, 3 Drawing Figures TANK PATENTEDum 24 1912SHEU 1 [1F 2 1 DOUBLE-ACTING TANDEM PISTON PUMP RELATED APPLICATION Thisapplication is a division of my application entitled Catch Basin andSewer Pipe Cleaner," U.S. Ser. No. 857,424 filed Sept. 12, 1969, now US.Pat. No. 3,658,589, granted Apr. 25, I972.

BRIEF SUMMARY OF THE INVENTION In my aforesaid parent application, thereis described and claimed a single vehicle for vacuum cleaning of catchbasins and flushing of sewer pipes with water surged through a hose andnozzle at pressures of about 2,000 to 3,000 pounds per square inchcausingthe hose to jump and move the nozzle for seeking its way aroundand through obstructions in a sewer pipe or the like in the manner of ajack hammer. The present invention now relates to the double-actingtandem piston pump disclosed in my parent application for producing thehigh pressure surging of water through the hose and nozzle.

The tandem piston pump of this invention is mounted on the singlevehicle disclosed in my parent application and has a first pistonreciprocated by pressurized oil from a hydraulic pump convenientlydriven through a conventional power take-off from the vehicle engine.This first piston reciprocates a second piston to surge water from thevehicle tank through a hose which is reeled on the front of the vehicleand carries a self propelling nozzle on its leading end.

The tandem piston water pump of this invention forces water through thehose at pressures of 2,000 to 3,000 pounds per square inch, but as thepumping piston reaches the end of its stroke and is reversed, there is amomentary lull in the water flow creating a pulsing action which causesthe hose to jump and moves the nozzle to seek its way around and throughobstructions in the manner of a jack hammer.

Since the tandem piston pump is hydraulically driven, it can beconveniently located anywhere on the vehicle close to or remote from anengine driven oil pump and driven at any rate controlled by the pressureof the hydraulic fluid.

In its preferred embodiment, the double-acting tandem piston pump ofthis invention has a central body portion with cylinders of the same ordifferent diameters extending from both sides thereof. A piston rodextends through the central body into both cylinders and piston headsare secured on the ends of the rod. One of the pistons is actuated byoil from the engine driven pump to drive the other piston for surgingthe water at high pressure. A feature of the invention includes acontrol rod slidable in a recess in the piston rod and extending throughthe head of the oil cylinder to trip a switch controlling a valve whichcontrols oil flow to and from the opposite ends of the oil cylinder.This control rod is pushed to a switch tripping position by the pistonrod and is ejected to a further extended position by the oil pressureintroduced into the end of the cylinder for reversing the piston stroke.Then when the oil piston reaches the end of its stroke remote from thecylinder head, the control rod is pulled from its extended position to alocked retracted position permitting the switch to return to an initialposition for reversing the oil flow control valve. The control rod thusonly has a short stroke being moved only when the oil piston ap proachesthe ends of its stroke.

It is then an object of this invention to provide a tandem pump having adriving piston actuated hydraulically from a rotary pump and a drivenpiston delivering high pressure water at surging flow rates.

A further object of this invention is to provide a douhie-acting tandempiston pump with a driving piston in a first cylinder of a selected sizeand a driven piston in a second cylinder of selected size connected by acommon piston rod which trips a control rod to effect reversal of thestroke of the pistons.

A further object of the invention is to provide a double-acting pistonpump with a common central body, cylinders of selected sizes on oppositesides of the body, pistons slidable in the cylinders connected by acommon piston rod extending through the body, and a control rod actuatedfrom the piston rod for effecting reversal of flow of pressurized fluidto opposite sides of the driving piston which control rod is urged bydriving fluid pressure on one side of the piston to an extended positionand pulled to a retracted locked position by the piston rod.

A still further object of the invention is to provide an oil trapprotecting the control rod against impact when driven to its extendedposition.

Other and further objects of this invention will be apparent to thoseskilled in this art from the following description of the annexed sheetsof drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of thewater and oil circuits for the tandem pump which is illustrated inlongitudinal cross-section;

FIG. 2 is a broken longitudinal cross-sectional view of the tandempiston pump of this invention;

FIG. 3 is a view similar to FIG. 2 but on a section line 90 therefromand showing the pistons at the opposite ends of their stroke.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The tandem pump of thisinvention is conveniently mounted on the catch basin and sewer pipecleaning vehicle disclosed in my aforesaid parent application, Ser. No.857,424, and receives water from a tank diagrammatically illustrated at12 in FIG. 1 to surge the water through a hose diagrammaticallyillustrated at 28 with a high pressure self-propelling spray nozzle 29on its front end and having a hollow head 30 with rearwardly openingorifices.

This pump 60 has a central cylindrical body 61 with a first cylinder 62extending from one side thereof and a second cylinder 63 extending fromthe other side thereof. These cylinders can be of the same or differentdiameters for a purpose to be more fully hereinafter described.

The cylinder 62 has an end head 64 thereon. The cylinder 63 has an endhead 65 thereon.

As best shown in FIGS. 2 and 3, a piston rod 66 extends through thecentral body 61 into both the cylinders 62 and 63. A first piston head67 is secured to an end of the piston rod 66 in the cylinder 62, and asecond piston head 68 is secured to the opposite end of the rod in thecylinder 63. Piston rings 69 are carried in grooves in the piston 67 andsealingly engage the cylinder wall 62. Similar piston rings 70 arecarried in grooves in the piston 68 and engage the cylinder wall 63.These piston rings include a plastic ring body with a groove in the endwall thereof facing the cylinder chamber receiving an O-ring whichsealingly connects the end face of the ring with the piston ring grooveand which causes an expansion of the ring body against the cylinder wallunder the influence of pressure in the cylinder.

In the illustrated form of the pump 60 the piston 67 is the drivingpiston and is actuated by oil under pressure from an engine-drivenhydraulic pump. Oil is selectively circulated to and from opposite facesof the piston 67 through a first port 71 in the central body 61 and asecond port 72 in the end head 64. The piston 68 is the water pumpingpiston, and the cylinder 63 receives water into the opposite endsthereof from a common manifold 73 through a port 74 in the central body61 and a port 75 in the end head 65. Water pumped by the piston 68 isdischarged from opposite ends of the cylinder 63 into a common outlet 76from a first port 77 in the central body 61 and a second port 78 in theend head 65.

Packings 79 and 80 in the central body 61 sealingly engage the pistonrod 66 to prevent leakage between the oil and water sides of the pump.

As shown in FIG. 1, the inlet manifold 73 for the water side of the pumpreceives water from the supply tank 12 of the vehicle through a conduit81 and the water is discharged through the manifold 76 and hose 28 tothe nozzle 29.

Check valves 82 are provided in each of the ports 74, 75, 77 and 78.These valves are spring-loaded to closed positions, and are arranged inthe ports so that the valve 82 in the port 74 will be closed as thepiston is moved to the left-hand end of its stroke, while the valve inthe port 77 will be open to discharge the water being pumped into themanifold 76. At the same time the valve in the port 75 will be opened toadmit water to the right-hand side of the piston 68, while the valve inthe port 78 will be closed. The valves are operated by pressuredifferentials, with the water inlet valves opening on the suctionstroke, closing on the pressure stroke, and with the outlet valvesclosing on the suction stroke and opening on the pressure stroke. Thesevalves, therefore, alternately admit water from the supply tank toopposite sides of the piston and alternately discharge the water on thepressure stroke of the piston, with one inlet valve being opened on oneside of the piston and one discharge valve being opened on the oppositeside of the piston at the same time, while the other two valves areclosed.

The driving piston 67 alternately receives oil on opposite sides thereofthrough the ports 71 and 72, which act both as inlet and outlet ports.

As shown in FIG. 1, oil from a tank 83 on the vehicle is fed through anintake tube 84 to the inlet side of an engine-driven oil pump 85. Thispump discharges through a tube 86 into a four-port spring-centered spoolvalve diagrammatically illustrated at 87. This valve 87 is hydraulicallyactuated from a solenoid operated pilot valve 88. The solenoid valve 88is controlled from a master switch 89 supplying actuating current to areversing micro-switch 90 having one pole 91 actuating a solenoid 92 onone side of the valve spool in the pilot valve 88 and a second pole 93actuating a second solenoid 94 on the opposite side of the spool valve.

Oil from the tube 86 passes through the valve 87 to a tube 95,discharging to a pressure regulating valve 96 which dumps into a returntube 97 back to the tank 83. The valve 96 maintains a predeterminedpressure differential between the tubes 95 and 97.

The spool in the valve 87 is shifted by oil under pressure from chambers98 and 99 at opposite ends of the spool. These chambers selectivelyreceive oil at the pressure maintained by the valve 96 under the controlof the pilot valve 88. This pilot valve 88 has an inlet oil tube 100 inthe oil line 95 ahead of the valve 96 and an outlet oil tube 101downstream of the valve 96 so that the pilot valve only receives oilunder the pressure maintained by the valve 96. This oil is selectivelyfed under control of the pilot valve 88 through a tube 102 to thechamber 98 and through a tube 103 to the chamber 99. With the leaf a ofthe microswitch in the position shown in FIG. 1, current flows throughthe wire 91 to energize the solenoid 92, thus shifting the spool in thevalve 88 so that oil from the tube 100 will flow to the tube 102 andchamber 98 for forcing the spool in the valve 87 to the right. At thesame time oil in the chamber 99 will be drained back through the tube103, through the valve 88 to the return line 101 back to the tankthrough the tube 97 The valve 87, when shifted by oil under pressurefrom the chamber 98, will communicate the pump pressure tube 86 to theport 72, while at the same time opening the port 71 to the tube andthrough the pressure valve 96 back to the tank 83. Oil under the fullpressure of the pump 85 will thereby be introduced to the left-hand sideof the cylinder 62, forcing the piston 67 to the right. When the pistonreaches the right-hand end of its stroke, as shown in FIG. 3, the leaf90a of the micro-switch 90 returns to its opposite pole and energizesthe line 93, which activates the solenoid 94 and reverses the pilotvalve 88 so that oil from the pressure line will flow to the line 103and to the chamber 99, while oil from the chamber 98 will flow throughthe tube 102 into the line 101 back to the tank. The valve 87 willthereupon be shifted so that oil is fed under pressure to the port 71and drained from the port 72.

The micro-switch activating means is shown in FIGS. 2 and 3, andincludes a control rod 104 freely mounted in an axial recess 105 in theleft-hand end of the piston rod 66. The rod 104 slides freely through acap 106 which is threaded in the end of the piston rod 66 and is adaptedto allow high pressure oil from the port 72 to flow into the recess 105.The rod 104 has a head 107 on its inner end adapted to bottom atopposite ends of the piston rod stroke respectively on the cap 106 andon the end wall 1050 of the recess 105. A reduced diameter integral rodportion 108 slides through a gland 109 in the end head 64 and provides ashoulder 110 in which port 72. The gland 109 has a recess 111 exposed tothe port 72 and confronting the shoulder 1 10.

The reduced diameter portion 108 of the control rod 104 projects beyondthe end head 64 and has an enlarged head 112 thereon slidably mounted inan openended cylinder 113 which is secured to the outer face of the endhead 64. In the position illustrated in FIG. 2 the end wall 105a of therecess has just pushed the control rod 104 to move this head 112 to itsextended posimmm tion projecting beyond the cylinder 113. In thisextended position the head 112 has tripped the switch leaf 90a,admitting oil to the port 72, thus starting the piston on its stroke tothe right. Since the head end 107 of the rod 104 is exposed to the highpressure in this port 72 while the other head end 112 of the rod 104 isexposed to the atmosphere, the rod 104 is driven further outwardly,moving the shoulder 110 into the recess 11], where trapped oil in thisrecess will prevent the shoulder from impacting against the gland 109.The rod will remain in its extended position, with its head 112 againstthe switch leaf 900 until the cap 106 engages the head 107 at theinboard end of the piston stroke, as shown in FIG. 3. Then the head 112of the control rod 104 will be pulled into the cylinder 113 to aposition where a peripheral grove 114 in the head is aligned withspring-loaded ball-bearings 115 carried by the cylinder. Thesespring-loaded ball bearings or detents will snap into this groove 114for holding the control rod 104 in a retracted inward position, as shownin FIG. 3.

In the position of FIG. 3 the head 112 has been withdrawn into thecylinder 113 sufficiently to allow the spring-loaded leaf 90a of themicro-switch to move to the right and change the pole position of theswitch. The control rod will remain in the position of FIG. 3, held bythe detents 115 until it is again pushed by the recessed end wall 150a,returning the rod to the position of FIG. 2 for the next stroke.

In the position of FIG. 8, fluid is just beginning to enter the port 71to start the piston on its stroke to the left.

In the position of the leaf 900, shown in FIGS. I and 2, thesolenoid-actuated pilot valve 88 feeds oil under the differentialpressure maintained across the valve 96 to position the main valve 87 sothat oil will flow into the port 72 and out of the port 71. This, ofcourse, will drive the piston 67 to the right-hand end of the cylinder62, whereupon, as shown in FIG. 3, the cap 106 will engage the controlrod head 107, retracting the head 112 into the cylinder 113 to aposition where it is retained by the spring pressed detents 115. Ofcourse, upon reversal of the pole position of the micro-switch to theposition of FIG. 3, the pilot valve 88 will again be energized toreverse the main valve 87 and introduce pressurized oil into the port 71and out of the port 72, thereby moving the piston 67 to the left.

It will be appreciated that while the stroke of the piston rod 66 may bequite long, the control rod 104 is only shifted a short distance, justsufficient to throw the leaf 90a of the micro-switch 90 between itspoles. Thus, when the piston rod 66 moves to the right from the positionof FIG. 2, the rod 104 will remain stationary, being retained in itsextended position by oil pressure in the port 72. Then when the pistonrod 66 moves to the inboard end of its stroke, as shown in FIG. 3, thehead 107 will be engaged by the cap 106, pulling the rod 104 therewithonly until the head 112 is moved into the cylinder 113 sufficiently toalign the groove 114 with the spring-pressed detents 115. For example,the control rod 104 may only be shifted 1 inch or so in installationswhere the piston rod 66 is shifted 15 inches or more.

As illustrated, the cylinders 62 and 63 are of the same diameter, but ifit is desired to increase the flow capacity of the water pump, thecylinder 63 and piston 68 can be of a larger diameter than the cylinder62 and piston 67. Conversely, if it is desired to obtain a highermaximum water pressure, the cylinder 62 and piston 67 can be larger thanthe cylinder 63 and piston 68.

From the above descriptions of the pump 60 it will be understood thatthe engine-driven oil pump operates through a pilot valve and a mainvalve to alternately deliver pressurized oil into the opposite ends ofthe cylinder 62. When oil is delivered into one end of the cylinder 62,it is simultaneously drained from the other end of the cylinder 62.This, of course, reciprocates the piston 67 which, in turn, drives thepiston 68. Water is supplied from the tank 12 altemately to oppositesides of the piston 68, and when one side of the piston is on the intakestroke, the other side is on the pressure stroke, and the water isdelivered under pressure to the hose 28. Very high pressures may bedeveloped in the chamber of the oil cylinder 62 to deliver water undervery high pressures. These high pressures will be maintained, althoughthere is a momentary lull or dwell in the water flow as the pistonsreverse their stroke. As a result, the water is delivered to the hose ata high pressure, but at a flow rate which drops rapidly at the end ofthe stroke and then picks up very rapidly. This causes the hose 28 tojump, and effects the jack-hammer driving of the nozzle 29.

I claim as my invention:

1. A tandem pump which comprises a central body, a cylinder of selecteddiameter mounted on and extending axially from each side of said body, apiston head in each cylinder in sealed relation therewith, a piston rodslidably mounted in said body having its ends secured to the pistons insaid cylinders, inlet ports at both ends of one cylinder, separateoutlet ports at both ends of said one cylinder, valves in said inlet andoutlet ports admitting fluid to the cylinder on the suction stroke ofthe piston and discharging said fluid on the opposite side of thepiston, combination inlet and outlet ports on the opposite ends of theother cylinder, means for selectively introducing fluid under pressureinto one of said combination ports to reciprocate the piston in thecylinder between the ports, a control rod means controlled from thepiston rod for controlling the flow of the pressured fluid to and fromthe combination ports whereby reciprocation of the piston by thepressurized fluid will reciprocate the piston in said one cylinder toalternately surge fluid through one and then the other of said outletports, mechanical means holding said control rod in a retracted fixedposition during one stroke of the piston between the combination ports,and fluid pressure actuated means holding the control rod in an extendedfixed position during the opposite stroke of said piston.

2. The pump of claim 1 wherein said means reversing flow through thecombination inlet and outlet ports includes a solenoid actuated pilotvalve tripped at the ends of the stroke of the piston rod and a highpressure oil valve actuated by the solenoid valve for controlling flowto and from said combination ports.

3. A tandem piston pump effective to surge water through a hose andself-propelling nozzle on the leading end of the hose to cause the hoseand nozzle to jump at periodic intervals which comprises a central body,first and second cylinders of selected diameters each secured to anopposite side of said central body and extending coaxially therefrom,end heads on the outer ends of said cylinders, a piston rod slidablymounted in the central body and extending into both cylinders, pistonsslidably mounted in the cylinders secured on the ends of the piston rod,a water inlet port in said body communicating with the inner end of thefirst cylinder, a water inlet port in the end head of said firstcylinder communicating with the outer end of said first cylinder, awater outlet port in said body communicating with the inner end of saidfirst cylinder, a water outlet port in said end head of said firstcylinder communicating with the outer end of said first cylinder, valvesin each of said inlet ports opening on the suction stroke of the pistonin said first cylinder, valves in said outlet poi-ts opening on thepressure stroke of the piston in said first cylinder, a combinationinlet and outlet port in said central body communicating with the innerend of said second cylinder, a combination inlet and outlet port in theend head on said second cylinder communicating with the outer end ofsaid second cylinder, a pump delivering oil under pressure to andreceiving oil from said combination ports, a control rod controlled bysaid piston rod reversing oil flow through said combination ports toopposite sides of the piston in said second cylinder for reciprocatingthe piston to drive the piston in said first cylinder for surging wateralternately through said outlet ports, mechanical means holding saidcontrol rod in one fixed position during one stroke of the piston in thesecond cylinder, and oil pressure actuated means holding said controlrod in a second fixed position during the opposite stroke of said pistonin the second cylinder.

4. The pump of claim 3 wherein the means for reversing flow through thecombination ports includes an oil actuated spool control valveselectively venting oil to said combination ports and a solenoidactuated pilot valve tripped by the piston rod controlling the oilactuated spool valve.

5. A pump having a pair of opposed cylinders, a piston rod projectinginto both cylinders, piston heads on the ends of said rod, means forintroducing fluid under pressure alternately into the opposite ends ofone cylinder for reciprocating the piston therein to drive the pistonrod for reciprocating the piston in the other cylinder, said meansincluding an axial recess extending inwardly from the end of the pistonrod in the cylinder receiving the fluid under pressure, a cap on saidrecess, a control rod in said recess having a first head engaged by thepiston rod at one end of its stroke and by the cap at the other end ofits stroke, an end head on the cylinder receiving the fluid underpressure, a reduced diameter portion on said control rod sliding throughsaid end head in sealed relation therewith, a second head on the reduceddiameter control rod portion beyond the end head of the cylinder, asupplemental cylinder receiving said second end head in slidable relation, a groove in said second head, spring-pressed detents in saidsupplemental cylinder engaging in said groove to hold the control rod inretracted position, a switch engaged by the control rod in the extendedposition thereof, and said control rod being reciprocated at the ends ofthe stroke of the piston rod to trip said switch whereby the detentswill hold the control rod in stationary position between the ends of thepiston rod 6. 'fhe pump of claim 5 wherein the sea] for the control rodin the cylinder end head has a fluid trapping recess and the control rodhas a shoulder bottoming against fluid trapped in said recess to cushionthe outward driving of the rod through the end head.

7. In combination with a cylinder having an end head on one end thereof,a body at the opposite end thereof, a piston rod slidable through saidbody, and a piston on the piston rod in said cylinder, the improvementof a control device for regulating flow of oil under pressure intoopposite ends of the cylinder for reciprocating the piston whichcomprises said piston rod having an axial recess communicating with theend head end of the cylinder, a control rod having one end freelymovable in said recess and the other end slidable through said end headin sealed relation therewith, said control rod having opposed shouldersrespectively outside of said end head and inside of said end headlimiting sliding movement of the control rod through the end head, saidcontrol rod being pushed by fluid under pressure in the end head end ofthe cylinder to an extended position, means on the piston rod pullingthe control rod to a retracted position, means on the end head holdingthe control rod in said retracted position whereby the rod is locked infixed position except at the very ends of the stroke of the piston, andswitch means tripped by the end of the control rod each time it isshifted by the piston rod.

l l l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION ()ctober 24,1972 Patent No.

a, 700, 360 Dated Inventor(s) Roland E. ShaddOCk It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 4, line 55, cancel "which" and insert --the--.

Column 5, line 16, cancel "grove" and insert --groove--;

line 28, cancel "150a" and insert --l05a--.

Signed and sealed this 16th day of July 1971+.

(SEAL) Attest:

McCOY M. GIBSON, JR. Attesting Officer C. MARSHALL DANN Commissioner ofPatents FORM PO-lDSO (10-69) USCOMM DC owe-P69 n u s oovrnunzm PRINTINGorncr: Inn 0-!6l-33l

1. A tandem pump which comprises a central body, a cylinder of selecteddiameter mounted on and extending axially from each side of said body, apiston head in each cylinder in sealed relation therewith, a piston rodslidably mounted in said body having its ends secured to the pistons insaid cylinders, inlet ports at both ends of one cylinder, separateoutlet ports at both ends of said one cylinder, valves in said inlet andoutlet ports admitting fluid to the cylinder on the suction stroke ofthe piston and discharging said fluid on the opposite side of thepiston, combination inlet and outlet ports on the opposite ends of theother cylinder, means for selectively introducing fluid under pressureinto one of said combination ports to reciprocate the piston in thecylinder between the ports, a control rod means controlled from thepiston rod for controlling the flow of the pressured fluid to and fromthe combination ports whereby reciprocation of the piston by thepressurized fluid will reciprocate the piston in said one cylinder toalternately surge fluid through one and then the other of said outletports, mechanical means holding said control rod in a retracted fixedposition during one stroke of the piston between the combination ports,and fluid pressure actuated means holding the control rod in an extendedfixed position during the opposite stroke of said piston.
 2. The pump ofclaim 1 wherein said means reversing flow through the combination inletand outlet ports includes a solenoid actuated pilot valve tripped at theends of the stroke of the piston rod and a high pressure oil valveactuated by the solenoid valve for controlling flow to and from saidcombination ports.
 3. A tandem piston pump effective to surge waterthrough a hose and self-propelling nozzle on the leading end of the hoseto cause the hose and nozzle to jump at periodic intervals whichcomprises a central body, first and second cylinders of selecteddiameters each secured to an opposite side of said central body andextending coaxially therefrom, end heads on the outer ends of saidcylinders, a piston rod slidably mounted in the central body andextending into both cylinders, pistons slidably mounted in the cylinderssecured on the ends of the piston rod, a water inlet port in said bodycommunicating with the inner end of the first cylinder, a water inletport in the end head of said first cylinder communicating with the outerend of said first cylinder, a water outlet port in said bodycommunicating with the inner end of said first cylinder, a water outletport in said end head of said first cylinder communicating with theouter end of said first cylinder, valves in each of said inlet portsopening on the suction stroke of the piston in said first cylinder,valves in said outlet ports opening on the pressure stroke of the pistonin said first cylinder, a combination inlet and outlet port in saidcentral body communicating with the inner end of said second cylinder, acombination inlet and outlet port in the end head on said secondcylinder communicating with the outer end of said second cylinder, apump delivering oil under pressure to and receiving oil from saidcombination ports, a control rod controlled by said piston rod reversingoil flow through said combination ports to opposite sides of the pistonin said second cylinder for reciprocating the piston to drive the pistonin said first cylinder for surging water alternately through said outletports, mechanical means holding said control rod in one fixed positionduring one stroke of the piston in the second cylinder, and oil pressureactuated means holding said control rod in a second fixed positionduring the opposite stroke of said piston in the second cylinder.
 4. Thepump of claim 3 wherein the means for reversing flow through thecombination ports includes an oil actuated spool control valveselectively venting oil to said combination ports and a solenoidactuated pilot valve tripped by the piston rod controlling The oilactuated spool valve.
 5. A pump having a pair of opposed cylinders, apiston rod projecting into both cylinders, piston heads on the ends ofsaid rod, means for introducing fluid under pressure alternately intothe opposite ends of one cylinder for reciprocating the piston thereinto drive the piston rod for reciprocating the piston in the othercylinder, said means including an axial recess extending inwardly fromthe end of the piston rod in the cylinder receiving the fluid underpressure, a cap on said recess, a control rod in said recess having afirst head engaged by the piston rod at one end of its stroke and by thecap at the other end of its stroke, an end head on the cylinderreceiving the fluid under pressure, a reduced diameter portion on saidcontrol rod sliding through said end head in sealed relation therewith,a second head on the reduced diameter control rod portion beyond the endhead of the cylinder, a supplemental cylinder receiving said second endhead in slidable relation, a groove in said second head, spring-presseddetents in said supplemental cylinder engaging in said groove to holdthe control rod in retracted position, a switch engaged by the controlrod in the extended position thereof, and said control rod beingreciprocated at the ends of the stroke of the piston rod to trip saidswitch whereby the detents will hold the control rod in stationaryposition between the ends of the piston rod stroke.
 6. The pump of claim5 wherein the seal for the control rod in the cylinder end head has afluid trapping recess and the control rod has a shoulder bottomingagainst fluid trapped in said recess to cushion the outward driving ofthe rod through the end head.
 7. In combination with a cylinder havingan end head on one end thereof, a body at the opposite end thereof, apiston rod slidable through said body, and a piston on the piston rod insaid cylinder, the improvement of a control device for regulating flowof oil under pressure into opposite ends of the cylinder forreciprocating the piston which comprises said piston rod having an axialrecess communicating with the end head end of the cylinder, a controlrod having one end freely movable in said recess and the other endslidable through said end head in sealed relation therewith, saidcontrol rod having opposed shoulders respectively outside of said endhead and inside of said end head limiting sliding movement of thecontrol rod through the end head, said control rod being pushed by fluidunder pressure in the end head end of the cylinder to an extendedposition, means on the piston rod pulling the control rod to a retractedposition, means on the end head holding the control rod in saidretracted position whereby the rod is locked in fixed position except atthe very ends of the stroke of the piston, and switch means tripped bythe end of the control rod each time it is shifted by the piston rod.